Mathematics

In the figure, AB = AC and DB = DC. ∠ABD : ∠ACD is :

In the figure, AB = AC and DB = DC. ∠ABD : ∠ACD is : R.S. Aggarwal Mathematics Solutions ICSE Class 9.
  1. 1 : 2

  2. 2 : 1

  3. 1 : 1

  4. 1 : 3

Triangles

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Answer

In △ABC,

AB = AC

⇒ ∠B = ∠C = x ….(1) (let) (Angles opposite to equal sides in a triangle are equal)

In △BDC,

BD = CD

⇒ ∠DBC = ∠DCB = y ….(2) (let) (Angles opposite to equal sides in a triangle are equal)

Subtracting eq.(2) from (1), we have :

⇒ ∠B - ∠DBC = ∠C - ∠DCB

⇒ ∠ABD = ∠ACD

⇒ ∠ABD : ∠ACD = 1 : 1.

Hence, option 3 is the correct option.

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